Vibratory percussion rammers (hereinafter “rammers”) are used in the construction industry to compact soil and other loose materials. A typical rammer provides a generally vertical movement to a ground-engaging shoe that compacts the ground with a pounding type of movement. Conventional rammers include a motor-driven gearbox and a handle that is grasped by the operator. A percussion delivery unit is suspended from the gearbox and typically includes a ram and shaft assembly that extends downwardly from the gearbox into a guide cylinder, a spring box that extends upwardly into the guide cylinder, and a spring separator that is connected to the ram and shaft assembly and disposed in the spring box between upper and lower springs. The ram and shaft assembly is typically connected via a connecting rod and gear drive to the output shaft of an engine that is mounted on the gearbox. The ram and shaft assembly is driven to reciprocate up and down and the spring box is configured to reciprocate divergently relative to the reciprocations of the ram and shaft assembly. The lower end of the spring box typically carries the ground engaging shoe. Alignment of the percussion delivery unit is maintained by metal-on-metal contact surfaces such as between the ram and the guide cylinder, the spring box and the guide cylinder, (optionally, the shaft and the upper end of the spring box), and the spring separator and the interior of the spring box.
The assignee for this application, M-B-W Inc., manufactures and sells uniquely designed rammers that have low cost, easily replaced, non-metallic wear components including slide bearings and spring separators for reducing internal wear between high tolerance, costly reciprocating metal components, namely the ram and the guide cylinder, spring box and guide cylinder and the spring separator and spring box.
The present application derives from the inventor's recognition of problems associated with manufacture and use of the assignee's uniquely designed rammers and the unique wear components associated with these rammers. For example, the inventor has determined that the assignee's wear components are difficult to efficiently manufacture and install. The assignee's slide bearings are machined from extruded polyethylene tube to a size that will fit and function properly in the percussion delivery unit. Both the extrusion process and the machining process are expensive and time consuming. The combination of both processes is especially expensive and time consuming. The machining process is particularly difficult because the slide bearings are self lubricating, flexible, difficult to handle, chuck, and cut, and are subject to volumetric instability with temperature change. For the above reasons and because of the length of the wear surfaces between the guide tube and the ram and spring box assemblies, the inventor has found that it is difficult and not economically feasible to machine a single wear component or slide bearing from extruded polyethylene tube or other thin bearing material capable of reducing wear along the entire length of the delivery unit wear surface. Rather it has been necessary to make several relatively shorter slide bearings which are spaced or stacked together in series along the interior length of the guide tube. Each of these wear components must be separately extruded and machined, further adding to the cost and time of manufacture.
The inventor has also determined that its non-metallic slide bearings are subject to breakdown. For example, during rammer operation, a stacked series of slide bearings is subjected to friction and heat emanating from reciprocating components of the delivery system as well as heat generated by the engine, clutching mechanism and gear box. As heat increases, the slide bearings tend to expand and as heat decreases, the slide bearings tend to contract. Occasionally adjacent slide bearings are forced into each other, overlapping or deforming and seizing up the delivery unit. Also, as the slide bearings expand in response to the system heat, there is an increased likelihood of expansion beyond the limit provided for in the machining of adjacent metal components, thereby seizing up the delivery unit. These breakdowns require the owner to disassemble the machine, replace the disfigured slide bearings, and reassemble the machine, thus costing time and money.